Catalytic Activity and Kinetic Studies of Core@Shell ......core@shell nanostructures was found as 258 m2/g for 10 wt. % TiO 2 photocatalyst. A decrease in surface area has been observed

Mutawara Mahmood Baig et al., J.Chem.Soc.Pak., Vol. 42, No. 04, 2020 531

Catalytic Activity and Kinetic Studies of Core@Shell Nanostructure NiFe2O4@TiO2 for

Photocatalytic Degradation of Methyl Orange Dye

Mutawara Mahmood Baig, Erum Pervaiz, Muhammad Junaid Afzal 1Department of Chemical Engineering, School of Chemical & Materials Engineering (SCME),

National University of Sciences & Technology (NUST), Islamabad, Pakistan [email protected]*

(Received on 25th Feb 2019, accepted in revised form 11 October 2019)

Summary: Current research focuses on synthesis and characterization of magnetically separable

core@shell (NiFe2O4@TiO2) nanostructured photocatalyst with different weight percent (10, 20, 30, and 40) TiO2 using simple wet chemical techniques. Magnetic core with TiO2 shell was

synthesized by the hydrolysis of TTIP precursor with NiFe2O4 nanoparticles. NiFe2O4 nanoparticles were synthesized by the sol-gel auto combustion method. The synthesized nanostructures were

characterized for structural, morphological and magnetic behavior using XRD, TEM, SEM and VSM while the surface area was calculated using Brunauer-Emmett-Teller analyzer. Pure nickel

ferrite was indexed as spinel FCC crystal structure while anatase titania was confirmed from the characteristic peaks in the indexed XRD patterns. SEM images show the uniform particle size and

spherical morphology with average size of 18.85 nm±2nm. The Surface area of prepared core@shell nanostructures was found as 258 m2/g for 10 wt. % TiO2 photocatalyst. A decrease in

surface area has been observed with the increase in TiO2 percentage. The photo-catalytic degradation of MO was studied using UV-Visible spectroscopy under NiFe2O4-TiO2 catalyst. UV-

spectra revealed degradation of methyl orange by the decrease in the characteristic peak at 460 nm. Kinetics of degradation reaction were studied by the integral method of analysis using UV

absorbance data at 460 nm. The photo-catalytic activity of as synthesized catalyst was enhanced many folds as compared to the pure nickel ferrite. M-H curves obtained from VSM revealed a

decrease in the magnetization of nickel ferrite with a coating of non-magnetic TiO2.

Keywords: Photocatalysis, Magnetic nanoparticles, Core-shell nanostructures, Spinel ferrites, Titania.

Introduction

Textile industry shares a significant part in

water pollution by adding a variety of organic and

inorganic dyes in wastewater that needs to be treated

before its mixing with fresh water streams. Increasing

pollution problems emerged a need to find a solution

that is cost effective, recyclable and reliable. As this is

the era of nanomaterials, so research is being carried out

worldwide to fabricate materials that can help in the

efficient removal of pollutants from the environment as

well as wastewater. Due to the large surface area and

diverse properties, nanomaterials are tunable for many

applications, including electronics, biomaterials, energy,

and environment [1-3]. Spinel ferrites (AB2O4) are one

of the ceramic oxides, which exhibit huge compositional

diversity, chemical and thermal stability and hybrid

electrical & magnetic character at the same time [4].

Thus, the inert behavior of spinel ferrite has increased its

usage as a catalytic material. In the past few decades,

solar energy such as photocatalysis has been used as a

wider solution for water-based organic dyes. The

photocatalytic technology has been demonstrated to be

effective for waste and drinking water treatment, water

disinfection, photoreduction of carbon dioxide or

nitrogen and many other applications [5]. Advance

oxidation processes (AOPs), rely on the generation of

highly reactive and oxidizing hydroxyl radical (•OH),

are promising techniques for water treatment processes

because of their exemplary performance on toxin

reduction, low cost and photochemical stability [6].

Metal oxide nanostructures are widely employed in

numerous applications [7-12] including AOPs because

of their remarkable physicochemical properties [13]. A

number of oxides, noble metals, and composites of

oxides have been employed as photocatalysts. However,

effective photocatalysis with good percent degradation

of dye and activity remains a challenge. Therefore, a

need is there to use the materials in combination to

exploit their properties. Core@shell nanostructures have

drawn numerous interest these days because of their

fascinating uses in the field of magnetism, electronics,

and catalysis. Unlike single-component catalysts,

core@shell nanostructures are designed to integrate

multiple properties into a single system. Furthermore,

composites having a core of magnetic material are

conveniently extracted in a magnetic field.

Among numerous AOPs, titania is the most

commonly used catalyst in heterogeneous

photocatalysis, due to its photostability, nontoxicity,

competitive cost, and is stable in water under severe

*To whom all correspondence should be addressed.

mailto:[email protected]


environmental circumstances. It is also an excellent

inorganic semiconductor and has environmental as well

as temperature stable dielectric properties [4]. A number

of research papers regarding applications of the

magnetic nanomaterials containing titanium dioxide

have been reported [14-31]. Nevertheless, until now,

maximum research has concentrated on the titania based

nanoparticles for photocatalysis applications [14-22].

Since titania is an electrical insulator, the major problem

with its use in the applications mentioned above, is its

extraction from treated water. However, by using the

special methods, we can synthesize core@shell

nanoparticles comprising a core of magnetic material

and a shell of photocatalytic material and the problem of

catalyst recovery can be solved by using the small

magnetic field.

Hence, synthesis of titania photocatalyst

having a core of magnetic material has provided a route

of resolving the problems linked with the extraction of

titania photocatalyst from the treated water. However, it

is not easy to synthesize core@shell nanostructure of

titania particles with ultraviolet light photo-activity

without losing the magnetic features. Nowadays,

transition elements such as nickel, cobalt, iron and

strontium are used as core materials. As these metals are

more stable, they show excellent results in the

degradation of organic compounds. Kim et al. [32]

synthesized NiFe2O4 - TiO2 nanoparticles by using wet

chemical method for photocatalytic hydrogen synthesis.

Misra et al. [14] synthesized anatase TiO2@NiFe2O4

system by using reverse micelle and hydrolysis

approach with enhanced photocatalytic activity, but

these core@shell nanostructures retained the properties

of non-coated NiFe2O4. Therefore, synthesis of

impeccable MFe2O4@TiO2 (M = Fe, Sr, Ni, Co, Cu)

nanostructures requires more investigation.

The core objective of this research was to

synthesize core@shell structured NiFe2O4@TiO2

photocatalyst havig enhanced photocatalytic activity for

degradation of organic dyes. NiFe2O4@TiO2

photocatalyst was synthesis by hydrolysis of a titanium

isopropoxide (TTIP) precursor in the presence of

NiFe2O4 nanostructure, whereas NiFe2O4 NPs were

synthesized by sol-gel approach. Characterizations of

the NiFe2O4@TiO2 photo-catalyst were examined by

XRD, SEM, TEM, while BET analysis was carried out

for surface area measurement. UV–visible spectroscopy

was used to examine the light absorbing activities of the

catalyst. VSM was used to investigate magnetic

behavior of the nanoparticles. In addition, kinetic study

and catalytic activity of photocatalyst were also

investigated.

Experimental

Synthesis of the core@shell nanostructure

NiFe2O4@TiO2 photocatalyst

The core@shell nanostructure was synthesized

by sol-gel approach shown in Fig. S1 (supporting

information). In (a) step 1, to prepare core material

NiFe2O4, iron nitrate [Fe (NO3)3•5H2O], (Sigma-

Aldrich) and nickel nitrate [Ni (NO3)2•6H2O], (Sigma-

Aldrich) were used as the Fe and Ni precursors,

respectively, and distilled water as a solvent. Aqueous

solutions of iron nitrate and nickel nitrate were prepared

by adding 0.2 mol of iron nitrate and 0.1 mol of nickel

nitrate in a solvent. The molar ratio of salts M3+/M2+ was

kept at 2:1. Aqueous solutions of salts were mixed at

room temperature and stirred until the mixture was

homogenized. The aqueous solution of a chelating agent

was prepared by adding 0.15 mol of citric acid and

mixed with the nitrate solution. The mixture is then

stirred for 1 h followed by neutralization with aqueous

ammonia to ensure the hydrolysis of Fe and Ni

precursors. The final solution was then evaporated at

80ᴼC until a vigorous gel was formed. The gel was

further prone to heat so that the auto combustion starts,

and a fluffy like powder was formed. The powder was

dried in an oven at 100ᴼC for 2h. The obtained powder

was calcined at 600ᴼC for 4 h to produce cubic

crystalline NiFe2O4 nanoparticles. In (b) step 2, the

titania was coated on magnetic core NiFe2O4 as follows:

Briefly, 0.15 g of as-synthesized NiFe2O4 nanoparticles

and 0.15 g of cetyl trimethyl ammonium bromide

(CTAB) was added into 135 ml (8:1 volume) of n-

butanol and anhydrous ethanol solution. The solution is

subjected to sonication for 30 min to ensure the

complete dispersion of nanoparticles; a few drops of 2

wt. % nitric acid-water solution was added into a

mixture. Then 0.12 moles of TTIP in anhydrous ethanol

were added dropwise with controlled rhythm in a

mixture at room temperature. The weight content of

titania was increased in mixture as 10%, 20%, 30% and

40% (w/v %), respectively. The final mixture was

further subjected to sonication for 4 h at 75ᴼC. The

resulting nanoparticles were then centrifuged and

washed with anhydrous ethanol, repeatedly. The

precipitates were dried in an oven for 24 h at 100ᴼC.

The anatase shell TiO2 coated NiFe2O4 was obtained

after being calcined at 500ᴼC for 2 h.

Characteristics of the core@shell NiFe2O4@TiO2

photocatalyst

Synthesized NiFe2O4 and NiFe2O4@TiO2

nanoparticles were subjected to XRD (STOE-Seifert


X’Pert PRO) using CuKα radiation (λ = 1.5406 ᴼA) at

2θ angles from 20ᴼ to 80ᴼ. SEM (JEOL-instrument

JSM-6490A) executed the morphological study. BET

analysis was performed for surface area analysis. The

UV-Visible spectra of photocatalyst were obtained by a

spectrophotometer (T60 PG Instruments, UK), over the

range of 300-900 nm.

Photocatalytic activity

The photocatalytic activity was determined by

the photocatalytic degradation of methyl orange dye

under a UV lamp. The reaction suspension was prepared

by adding 1 mg MO and 0.1 g photocatalyst

NiFe2O4@TiO2 in 125 ml distilled water. The photo-

catalytic degradation of methyl orange was performed at

ambient temperature. The resulting aqueous solution,

comprising the catalyst and the methyl orange, was

stirred and placed under UV lamp (300 W Xenon) with

cutoff filter 400 nm with the lamp switched off. For the

initiation of the photochemical reaction, the lamp was

switched on. Samples for analysis (3 ml) were taken

after a fixed time interval and centrifuged to separate the

photocatalyst. The UV spectrophotometer was used to

measure the absorbance of methyl orange dye at given

time interval.

Results and Discussion

Structural analysis of NiFe2O4and NiFe2O4@TiO2

Fig. 1 shows the indexed XRD patterns of pure

NiFe2O4 and TiO2 coated NiFe2O4 nanoparticles

prepared using sol-gel auto combustion technique (10%,

20%, 30% and 40% weight content of TiO2). The

broader XRD peaks indicate that the particles have

small crystallite sizes and are in nanoscale. It can be

observed in Fig. 1 (a) that well phase pure crystalline

spinel nickel ferrite has been synthesized with

characteristic peaks at 2θ values of 30.278 (d220), 35.645

(d311), 37.309 (d222), 43.346 (d400), 49.463 (d331), 54.043

(d422), 57.408 (d511), and 63.014 (d400) indicating a cubic

spinel crystal structure [JCPDS card no 77-0426].

Except for the impure phase of α-Fe2O3 (hematite),

which is found in all samples. XRD patterns in Fig. 1

(b-e) can be easily indexed as anatase titania comprises

of peaks at 2θ values of 25.237 (d101), 37.701 (d004),

48.057 (d200), 54.003 (d105), 55.064 (d211), 62.799 (d204),

70.29 (d220), and 75.127 (d215) [JCPDS card no 04-

0477]. NiFe2O4@TiO2 did not contain NiFe2O4 peaks,

which shows that the TiO2 is completely coated with

NiFe2O4 nanoparticles. However, two small peaks at 2θ

values of 35.685 (d311), 37.329 (d222) were identified,

indicating the presence of NiFe2O4. The full width at

half maximum (FWHM) values has been used

to calculate the crystallite sizes using hkl values and d-

spacing. Crystallite sizes were calculated by Debye-

Scherrer’s equation from the most intense peaks.

(Where, λ represents wavelength of

incident X-rays, k represents shape factor, β represents

FWHM in radian while θ represents angle of

diffraction). Crystallite sizes were found to be 14 nm ± 2

nm for pure nickel ferrite and 12nm ± 1 nm for titania

coated core@shell nanoparticles respectively.

Fig 1: The XRD patterns of NiFe2O4 and

NiFe2O4@TiO2 photocatalyst.

Morphological and elemental analysis

Fig. 2 (a-d) shows the SEM images of titania

coated nickel ferrite core@shell nanoparticles. SEM

determined the morphology and the particle size of the

samples at a magnification of 60,000, in which a powder

sample was analyzed with dispersion treatment. The

morphological analysis revealed that the nano-sized

NiFe2O4@TiO2 are homogeneous, spherical in shape,

uniformly distributed and less agglomerated

nanoparticles. Average particle size was found in the

range of 16 nm to 24 nm. Elemental composition of the

prepared core@shell nanoparticles was found using the

inbuilt EDX analysis as shown in Fig. 3 (a) and Table

S1 (supporting information). EDX analysis shows

composition and mass percentages of constituting

elements. It confirms the presence of Ni, Fe, Ti and O

atoms. EDX produced atomic ratio for Ti:Fe:Ni in

NiFe2O4@TiO2 catalyst of 0.17:2.75:1.56. Further,

atomic percentages can be verified in elemental X-ray

mapping as shown in Fig. 3 (b). The micrographs reveal

the homogenous distribution map of the constitute

elements of the sample.


Table-1: Surface area, pore volume, pore size and dye degradation efficiency of photocatalyst. Parameters Value (w/v %)

10% TiO2 40% TiO2

Surface area SBET, m2/g 257.8608 51.896

Pore volume, cm3/g 2.49956 0.4982

Pore size, Aᴼ 387.738 469.1847

Degradation efficiency, % 72.69 90.06

Fig. 2: SEM photographs of NiFe2O4@TiO2.

Fig 3: a) The EDX determined atomic composition of NiFe2O4@TiO2, b) EDX Mapping (Element

distribution images), c) TEM photographs of NiFe2O4@TiO2, d) ED pattern of NiFe2O4@TiO2.


Fig 4: Nitrogen adsorption-desorption isotherm of the photocatalyst. a) NiFe2O4@TiO2 (10%), b)

NiFe2O4@TiO2 (40%). (c-d) Pore volume and Pore size distribution analysis of both samples

respectively.

The morphology of the TiO2 coated nickel

ferrite was further confirmed by TEM. The TEM

micrographs are shown in Fig 3 (c). It can clearly

observe from the TEM images that the magnetic nickel

ferrite is dispersed in TiO2 coated matrix. The observed

particles are rough and irregular in shape. This is to be

expected since the ferrite synthesis uses combustion

step. The average particle size was found in the range of

14 nm to 20 nm. The typical ED ring pattern of

NiFe2O4@TiO2 is also shown in Fig 3 (d). The

concentric fringes show that the nano-catalyst is

polycrystalline in nature.

Surface area analysis

The surface area of NPs is determined by

using Brunauer-Emmett-Teller (BET) analysis by

nitrogen adsorption-desorption technique. Nitrogen

adsorption was executed at 77K in relative pressure

range of 0 to 1. N2 adsorption-desorption isotherm as

shown in Fig. 4 (a-b). A low hysteresis value for

adsorption and desorption of the coated core@shell

nanostructures can be observed from BET isotherms.

The BET surface area of nanoparticles was measured to

be 258 m2/g. The total pore volume of the samples was

measured by the nitrogen uptake at P/P0 = 0.96 by using

the Barrett-Joyner-Halenda (BJH) method (Fig. 4 (c-d)).

The structural parameters including the surface area

(SBET), total pore volume (Vtotal), and pore size (D) are

shown in Table 1. The larger the surface area, higher

will be the active sites, therefore, a high surface area is

critically important to enhance the redox reaction sites

[33]. The results show that increasing the amount of

titania led towards the reduction of surface area. This

decrease in surface area was due to thick layer of titania

shell on nickel ferrite with an increase in the percent

weight content of titanium isopropoxide.

Catalytic activity of NiFe2O4@TiO2 core@shell

nanostructures

UV-Vis spectroscopy is a powerful mean to

examine the light absorbing activities of powder

particles. Fig. 5 (a-d) shows the UV-Visible absorption


spectra of MO degradation with NiFe2O4@TiO2 in range

of 300 nm to 900 nm. The extent of reaction can be

measured using the change in absorbance intensity at

460 nm with time. After addition of the core@shell

nanoparticles, the reaction has been catalyzed and the

peak intensity observed to be decreased with time at 460

nm. This decrease in peak intensity observed to increase

while increasing the TiO2 percent in core@shell

nanostructures. Usually, the band gaps of

semiconductors are diligently associated with the

absorbed wavelength. A smaller band gap of a material

will have a larger absorption wavelength. Nickel ferrite

nanoparticles correspond to absorption band ranging

200 nm to 710 nm [32]. The result shows that the

NiFe2O4@TiO2 nanostructures for degradation of MO

dye exhibit continuous absorption band. The MO dye

with NiFe2O4@TiO2 nanostructures presented maximum

absorption at 460 nm. The absorption at 460 nm

indicates that that the absorption is edge active in a

visible region. A band gap (Eg) of NiFe2O4@TiO2

nanostructures was calculated from the equation;

Eg=hc/λ where “h” is a plank constant, “c” is speed of light =

2.988 × 108 ms-1, “λ” is cutoff wavelength at 460 nm

corresponding to the band gap of 2.69 eV. The

calculated band gap is smaller than pure TiO2 (3.2 eV).

Hence, the presence of NiFe2O4 nanoparticles improves

the absorbance of TiO2. It’s DC resistivity measured by

two-probe method observed to decrease with increase in

temperature as shown in the Fig. 7(a). Such

behavior can also be helpful as a photocatalytic material

because the empty conduction band and completely

filled valence band enhances the redox process under a

light that could enhance the photocatalytic activity [32].

Photocatalytic degradation and stability

Methyl-orange, belonging to the family of azo

dyes is extensively used in textile industry. In order to

observe the photo-catalytic activity of core@shell NPs

for degradation of MO, UV-Vis spectra were measured

at room temperature. The performance of core shell

nanoparticles is shown in Fig. 6(a). It can be seen that

the concentration of MO dye is inversely related to

irradiation time. The decrease in concentration of

methyl orange dye from ~25 μmol to ~4 μmol indicates

the degradation of the dye. The higher the amount as the

TiO2 in photocatalyst, the more will be the degradation

of dye occur. The photostability of the core@shell NPs

was determined by performing recycling photoactivity

test under UV lamp (300 W Xenon) with cutoff filter

400 nm and is shown in Fig. 6(b) It can be seen that

there is no significant loss in the photoactivity of the

core@shell NPs photocatalyst during ten successive

recycle runs, demonstrating that the excellent

photocatalytic efficiency of core@shell NPs.

Fig 5: UV-Visible spectra of a) NiFe2O4@TiO2 (10%), b) NiFe2O4@TiO2 (20%), c) NiFe2O4@TiO2 (30%),

d) NiFe2O4@TiO2 (40%).


Fig 6: a) MO degradation Curve, b) recycling photocatalytic degradation of MO over NiFe2O4@TiO2 (40%)

composite, c) transient photocurrent densities profiles of photocatalysts, d) cyclic voltammograms of

photocatalysts

Fig 7: a) Impedance analysis (Nyquist plots) for pure NiFe2O4 and NiFe2O4@TiO2 b) M-H curves for pure

NiFe2O4 and NiFe2O4@TiO2 (40% TiO2)


Mechanism of the photoactivity improvement

To further investigate the origin of

photoactivity enhancement of NiFe2O4@TiO2

photocatalyst than NiFe2O4 and the effect of

increasing contents of TiO2, a photoelectrochemical

analysis was performed [36-40]. Fig. 6(c) shows the

photocurrent of photocatalysts under periodic on/off

of irradiation (400 nm). Bare NiFe2O4 shows

approximately zero photocurrent response when the

light is ON, indicating a large bandgap of NiFe2O4.

Whereas as, with coting of TiO2, the NiFe2O4@TiO2

photocatalyst exhibits the photocurrent. As the

concentration of TiO2 is increased, the photocurrent

density is also increasing, indicating fast

photochemical reactions. Furthermore, the cyclic

voltammograms (Fig. 6(d)) of photocatalysts also

reveal that with the incensing percentage contents of

TiO2, a significant increase in current density is

achieved, which constitute the photocurrent response

test. Finally, the electrochemical impedance

microscopy was employed to monitor the charge

transfer resistance of the photocatalysts on the

electrode and at the electrolyte/electrode interface.

Fig 7(a) reveals that the NiFe2O4@TiO2 has a smaller

semicircle diameter than NiFe2O4, offering less

resistance to charge transfer and faster ion diffusion.

Hence, the above photoelectrochemical analysis

confirmed that the NiFe2O4@TiO2 photocatalysts

greatly improves efficiency by offering less

resistance to photogenerated electrons.

Kinetics of photodegradation reaction of methyl

orange

To find out the kinetics (n, k) of degradation

reaction, different methods can be utilized, like

differential and integral methods of analysis. An

integral method of analysis has been chosen to find

the kinetic parameters for degradation reaction of

MO dye. The relationship between the absorbance

(D) and the concentration (C) during the reaction is

given by

where C0 is the concentration at time t = 0, C is the

concentration at any time, and Ԑ is molar absorption

coefficients at a specified wavelength.

Substituting above equations in Langmuir-

Hinshelwood model [34],

The above equation reveals that the

absorbance tends to the value as that of expression in

terms of concentration after the completion of a

reaction (infinite time). The rate constant can be

found by the slope of ln (D∞-D0) vs time graph. The

same equation can be expressed in terms of

concentration.

Fig. S2 (a-d) (supporting information)

shows a plot of ln (D∞ – D0) vs time t. All

experimental data were well fitted to the first-order

kinetics of photo degradation reaction. The result

shows the first order kinetic behavior with rate

constant k1 = 0.2021 min-1. The photocatalytic

activity was determined by the formula [35].

The result shows (Table-2) that by

increasing the amount of titania the photocatalytic

activity of the catalyst is increased.

Table-2: % Photo catalytic activity of as synthesized

photocatalyst. Catalyst % Photocatalytic Activity

NiFe2O4@TiO2 (10%) 72.69

NiFe2O4@TiO2 (20%) 80.77

NiFe2O4@TiO2 (30%) 88.24

NiFe2O4@TiO2 (40%) 90.06

Magnetic analysis

Magnetic behavior and the magnetization of

pure nickel ferrite and titania coated nickel ferrites

have been measured using M-H loops under the

applied magnetic field of 10 kOe at room

temperature. Fig. 7(b) shows the required M-H

curves of synthesized samples and it can be observed

clearly that the magnetization value of pure nickel

ferrite has been decreased with a coating of titania

shell from 23 emu/g to 14 emu/g. This decrease can

be clearly subjected to the presence of non-magnetic

material in the powder, as a shell is comprised of

TiO2. This decrease in magnetization is not required

for separation of the catalyst, but still a good value of


magnetization can be used for the magnetic

separation of the synthesized core@shell nano-

catalyst. Ease of catalyst separation and reuse is one

of the major issues in heterogeneous catalytic

reactions that can be achieved using magnetic core

nanomaterials.

Conclusions

The core@shell nanostructures were

effectively synthesized by means of sol-gel auto

combustion approach. The XRD analysis confirms

the synthesis of pure phase nanocrystalline powders.

The crystallite sizes were calculated in the range of

12-14 nm±2 nm. The morphological analysis by SEM

reveals that the nano-sized NiFe2O4@TiO2 are

homogeneous, spherical in shape, uniformly

distributed and less agglomerated nanoparticles.

Average particle size was found in the range of 14.14

nm to 23.57 nm. The Brunauer-Emmett-Teller (BET)

analysis was done to measure the surface area of the

nanoparticles by nitrogen adsorption-desorption

technique. The BET surface area of nanoparticles was

measured to be 258 m2/g. The degradation of methyl

orange was photo-catalyzed by as synthesized

core@shell nanostructures and its photocatalytic

activity was evaluated to be 90.06%. The result

shows that the NiFe2O4@TiO2 nanostructures for

degradation of methyl orange dye exhibit a

continuous absorption band. The band gap of

NiFe2O4@TiO2 nanostructures was determined to be

2.69 eV. The calculated band gap is smaller than pure

TiO2 (3.2 eV). Hence, the presence of NiFe2O4

nanoparticles improves the absorbance of TiO2. The

integral method of analysis was used to study the

kinetic behavior of photochemical reaction. The

semi-log plot of dye absorbance versus time is linear,

indicating the first order photocatalytic reaction with

rate constant k1 = 0.2021 min-1.

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Documents

Catalytic Activity and Kinetic Studies of Core@Shell ......core@shell nanostructures was found as 258 m2/g for 10 wt. % TiO 2 photocatalyst. A decrease in surface area has been observed